1. Field of the Invention The present invention relates generally to a process for removing copper from a copper/ferrous scrap metal mix and, more particularly, to such a process which employs an oxidizing and chloridizing gas atmosphere operable to coat the ferrous scrap metal with a protective oxide coating while simultaneously chloridizing the copper until the copper is removed from the mix as a gas.
2. Description of the Prior Art
As is well known in the art, ferrous scrap is an important source of iron in steel making. However, with the increased use and recycling of ferrous scrap, the overall scrap quality is steadily decreasing. This is due in large part to the buildup of tramp elements such as copper which contaminate the scrap. Electric arc furnaces presently account for approximately 40% of the steel produced domestically on an annual basis, and these furnaces use 100% scrap metal as the charge source. It is apparent that ferrous scrap contaminated with tramp elements, particularly copper, makes an extremely inefficient charge material.
Presently, there is no really satisfactory process available for economically and efficiently removing copper in a recoverable form from solid ferrous scrap metal. In an article entitled "A New Low Temperature Process For Copper Removal From Ferrous Scrap", Iron & Steelmaker, November 1991, Vol. 18, No. 11, pages 61 through 68, coauthors A. W. Cramb and R. J. Fruehan disclose a process for removing tramp copper from solid ferrous scrap metal. However, the disadvantages of this process are that the process is energy intensive (i.e.--it must be conducted at 1,000 degrees C. or above) and the liquid matte used to remove copper tends to stick to the scrap metal which subsequently raises the sulphur content in the steel produced. The matte held by the scrap metal is processed with a hot acid wash to reduce its level, but this involves another unit operation at elevated temperatures which diminishes the economic value of the process. In addition, the sulphide matte and liquid wash acid must be dealt with after the process is completed.
Another process for removing tramp copper from solid ferrous scrap metal is disclosed in an article by K. Tokinori, H. Ohshita and M. Iwase, entitled "Removal Of Copper From Solid Ferrous Scrap By Using Molten Aluminum", 49th Electric Furnace Conference Proceedings, Vol. 49, Toronto Meeting, Nov. 12-15, 1991, at pages 113 through 120. Although following this process does permit copper to be removed from solid ferrous scrap metal, it also has disadvantages. For example, this process is also energy intensive as the process is reported to work best at 750 degrees C. In addition, the user is required to handle, process and work with molten aluminum.
As seen from the foregoing, although processes have been discussed for removing copper from solid ferrous scrap metal they are not without their shortcomings. Consequently, there is a need for an improved process for removing copper from solid ferrous scrap metal which allows the ferrous scrap metal to remain metallurgically intact while the copper is removed and recovered in economical fashion. This improved process should be capable of improving the overall quality of ferrous scrap metal and subsequently the quality of steel produced with ferrous scrap metal treated via the process.